The present invention generally relates to a device for supplying an air-fuel mixture to an internal combustion engine having at least two groups of cylinders provided with separate exhaust pipes, comprising a single carburation device supplying the mixture to a manifold feeding the two groups of cylinders through separate branches.
Such a device is frequently used in six or eight-cylinder V engines. The maximum torque available from the engine can be increased by using two separate exhaust pipes, instead of a single exhaust manifold.
The invention more particularly relates to supply devices of the above kind in which the richness of the air-fuel mixture supplied by the carburation device is regulated according to a characteristic of the exhaust gases of the engine. This characteristic is generally the composition of the exhaust gases, which may be determined from the signal supplied by an oxygen gauge placed in the exhaust gases. From the signal supplied by the sensor, the duty ratio of electrical pulses fed to electromagnetic valves controlling the passage of fuel or air to the engine may in particular be regulated so as to maintain the richness of the mixture supplied to the engine close to stoichiometry.
According to the invention, there is provided a fuel supply device for an internal combustion engine having at least a first group and a second group of cylinders, each group having a separate exhaust pipe, comprising a manifold header having two manifold branches each adapted for connection to the cylinders of a separate one of said groups; a carburettor connected to receive air and fuel and to deliver an air-fuel mixture to said manifold header, said carburettor, manifold header and manifold branches being so arranged that the branch associated with the first group receives an air-fuel mixture which is richer than the mixture received by the manifold branch of the second group; a first probe adapted to be located in the exhaust pipe of said first group for delivering a signal indicative of the composition of the exhaust gas of said first group; a regulation circuit associated with said probe and carburettor for controlling the air-fuel ratio delivered by said carburettor in dependence of said signal; and a correction circuit having a second probe adapted to be located in the exhaust pipe of said second group for delivering a signal indicative of the composition of the exhaust gas of the second group, fuel delivery means opening into the branch associated with said second group, and means for metering the fuel flow delivered by said fuel delivery means in dependence of the signal delivered by said second probe.
The means for metering fuel may typically comprise a solenoid valve placed in the fuel delivery means and an electronic control circuit connected to said valve and second probe and constructed to maintain the signal supplied by the second probe at a predetermined value.
The invention will be better understood from the following description of a particular embodiment of a fuel supply device.